Such a gasket is known from DE 100 65 202 A1.
Such a gasket may, in particular, be a cylinder head gasket that is adapted to be arranged between the cylinder head and the engine block of an internal combustion engine wherein, for example, the engine block contains a magnesium alloy and the cylinder head gasket includes at least one beaded functional layer which comprises a sheet metal layer made of spring steel for ensuring adequate spring elasticity of the sealing beading lines.
In this description and the accompanying Claims, a metallic material is nobler than another metallic material if its electro-chemical potential is higher than the electro-chemical potential of the other metallic material.
As an example, some values from the electro-chemical electromotive series are indicated in the following table, wherein the potential of the hydrogen normal electrode serves as a base factor (null point):
Mg/Mg2+−2.37 VAl/Al3+−1.66 V without oxide film−0.50 V with oxide filmZn/Zn2+−0.76 VCr/Cr2+−0.56 VFe/Fe2+−0.44 VNi/Ni2+−0.24 V.
Thus, iron having an electrochemical potential of −0.44 V is nobler than aluminium which has an electro-chemical potential of −1.66 V, and, in turn, aluminium is nobler than magnesium which has an electro-chemical potential of −2.37 V.
Due to its position in the electromotive series, it is to be expected that magnesium and its alloys will have a significantly greater tendency to corrode upon contact with spring steel compared with aluminium and its alloys, particularly as aluminium is frequently protected by a skin of aluminium oxide.
If, on the one hand, metallic materials having different electro-chemical potentials are in electrically conductive contact with one another and, on the other hand, both materials are in contact with an electrolyte (for example, a film of moisture consisting of water) then contact corrosion will occur.
DE 30 01 730 A1 discloses a cylinder head gasket consisting of three metallic sheets which are held closely together, wherein the fluid-tightness in the vicinity of water and oil passage openings is produced with the aid of cords or tapes of elastomer material that are firmly connected to the middle metal sheet and gasket the gap between the middle metal sheet and the engine block and also the gap between the middle metal sheet and the cylinder head when the gasket is installed.
EP 1 136 731 A2 discloses a single layer gasket for sealing the housing for an engine chain, wherein a flexible sealing element is arranged at the edge of an opening in the gasket for the passage of the chain.
U.S. Pat. No. 5,938,208 A discloses a cylinder head gasket consisting of beaded metal plates, wherein the beads are provided with a coating of a synthetic material.